1. Field of the Invention
The present invention relates to an image forming device including an intermediate transfer belt.
2. Related Art
A laser printer is one type of image forming device well known in the art for forming images on a recording medium. The laser printer forms images on the recording medium by first irradiating a laser beam on an electrostatic latent image carrying member, such as a photosensitive drum or a photosensitive belt, and subsequently developing this electrostatic latent image into a visible image with a developer, which is a toner formed of fine particles. The toner image is transferred to and fixed on a recording medium, such as a recording paper, to form a prescribed image.
A color laser printer for forming color images is provided with four colors of toner including cyan (C), magenta (M), yellow (Y), and black (BK). The color laser printer includes a single laser device, a single electrostatic latent image carrying member, and an intermediate transfer member, such as a transfer drum or a transfer belt, that contacts the electrostatic latent image carrying member.
A color printer having this construction forms an electrostatic latent image corresponding to each color, one color at a time, on the electrostatic latent image carrying member and develops the latent image into a visible image using toner for the corresponding colors. The visible image is first transferred to the intermediate transfer member, and this temporary transfer is repeated a total of four times for each color until a multicolored toner image including all four colors of toner is formed on the intermediate transfer member. Subsequently, a color image can be formed on a recording medium by transferring the multicolored toner image to the recording medium in a secondary transfer and fixing the toner thereon. Since all of the toner forming the toner image does not always transfer onto the recording medium, this type of printer includes a cleaning device for removing residual toner left on the intermediate transfer member following the secondary transfer operation. In the color laser printer described above, toner is not removed at the stage in which the four toner images are initially transferred to the intermediate transfer member. However, toner remaining on the intermediate transfer member after the toner image on the intermediate transfer member has been transferred to the recording medium in the secondary transfer must be removed. Therefore, the cleaning device is configured to remove only toner remaining on the intermediate transfer member that was not transferred to the recording medium by appropriately switching the cleaning device between a non-cleaning position for not removing toner and a cleaning position for removing toner. In general, the cleaning device is placed in the cleaning position by moving the cleaning device into contact with the intermediate transfer member and in the non-cleaning position by separating the cleaning device from the intermediate transfer member. An example of this type of cleaning device has been disclosed in Japanese unexamined patent application publication No. HEI-9-73240.
However, the cleaning device in conventional laser printers described above is not able to clean all the toner from the intermediate transfer member when the amount of residual toner is large.
For example, occasionally an error or the like occurs after multicolored toner images are transferred initially to the intermediate transfer member and before the multicolored toner image is transferred to the recording medium, causing a stoppage of the device. At this time, a large amount of toner meant to be transferred onto the recording medium remains on the intermediate transfer member. The cleaning device recovers this residual toner during an error-recovery process, but the amount of toner to be recovered in this case is larger than the normal process when cleaning residual toner after the toner image was properly transferred to the recording medium. When the amount of toner exceeds the capacity of the cleaning device to capture toner, the cleaning device suffers a drop in toner-removing efficiency. If toner remains on the surface of the intermediate transfer member after the cleaning process, the toner image formed in the previous printing operation will be superimposed on the toner image formed based on the new image data, generating ghost images and the like and resulting in a decline in image quality.